The present invention is generally related to detection of faulty conditions, and, more particularly, to a method for detecting electrical faulty conditions in power devices, such as solid state rectifiers, used in a propulsion system.
Vehicles that include an electrically-powered propulsion system typically use power devices, such as silicone-controlled rectifiers (SCRs), also known as thyristors, or other solid state devices, to connect a direct current (DC) power source to a DC power line filter. For vehicles that are operable on railroad tracts, e.g., locomotives and transit vehicles, the power source may be an external power source, e.g., a power rail, an onboard power source, e.g., an alternator driven by an internal combustion engine, or both, in a dual mode locomotive. The filtered power is used by traction inverters and other systems in the vehicle for driving traction motors and other electrical loads like blowers, fans, etc. In view of the relatively large power ratings of such systems, a single SCR may not be sufficient to carry the full power and multiple SCRs are generally connected in parallel to share the load. For example, in one exemplary dual mode locomotive there may be five or more SCRs connected in parallel during power rail operation. It will be appreciated that as the number of SCRs increases, the probability of any one of such power devices failing also increases. It is thus desirable to be able to provide techniques that quickly and reliably detect when respective ones of such power devices fail, such as may occur either in an electrically shorted condition or in an electrically open condition. This allows the operator of the vehicle to proactively arrange for repair and/or maintenance services that prevent potentially costly collateral damage to other components of the propulsion system.
Generally, the present invention fulfills the foregoing needs by providing in one aspect thereof, a method for detecting faults indicative of an electrical short condition in at least one power device of a propulsion system. The power device is connectable to an external direct current power source. Upon the power source being connected, the method allows to measure an initial voltage across a power line filter. Based on whether the initial voltage measurement is less than a predefined voltage threshold, the method allows to measure voltage developed across the line filter upon waiting a time interval. The method allows to determines the presence of the electrical short condition based on whether the magnitude of the voltage developed across the line filter rises to about power line voltage within the time interval, wherein the time interval is sufficiently short to avoid damage to the propulsion system and further wherein the time interval is sufficiently long relative to the time constant of the filter to enable said voltage to rise to about line voltage.
The present invention further fulfills the foregoing needs by providing in another aspect thereof, a method for detecting faults indicative of an electrical open condition in a respective one of a plurality of power devices of a propulsion system. The plurality of power devices is connectable in parallel circuit through a direct current (DC) link to an external DC power source. The method allows to determine the occurrence of high current events based on whether the value of DC link current is above a predefined current threshold. The method allows to monitor temperature of each power device connected to the power source and ambient temperature. The method allows to relate temperature of each power device to ambient temperature to determine the occurrence of the electrical open condition based on whether the difference between any respective power device temperature and ambient temperature remains within a predefined range during the high current event.
In yet another aspect thereof, the invention provides a method for detecting electrical faulty conditions in a plurality of power devices of a propulsion system. The plurality of power devices is connectable in parallel circuit through a direct current (DC) link to an external DC power source. The method provides a first sequence of actions for determining an electrical short condition in at least one of the power devices upon the power source being connected. The method further provides a second sequence of actions for determining an electrical open condition in a respective one of the plurality of power devices during the occurrence of high current events.